/*
 * Copyright 2016, Blender Foundation.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * Contributor(s): Blender Institute
 *
 */

/** \file eevee_mist.c
 *  \ingroup draw_engine
 *
 * Implementation of Blender Mist pass.
 * IMPORTANT: This is a "post process" of the Z depth so it will lack any transparent objects.
 */

#include "DRW_engine.h"
#include "DRW_render.h"

#include "DNA_world_types.h"

#include "BLI_string_utils.h"

#include "eevee_private.h"

extern char datatoc_common_view_lib_glsl[];
extern char datatoc_common_uniforms_lib_glsl[];
extern char datatoc_bsdf_common_lib_glsl[];
extern char datatoc_effect_mist_frag_glsl[];

static struct {
	struct GPUShader *mist_sh;
} e_data = {NULL}; /* Engine data */

void EEVEE_mist_output_init(EEVEE_ViewLayerData *sldata, EEVEE_Data *vedata)
{
	const DRWContextState *draw_ctx = DRW_context_state_get();
	EEVEE_FramebufferList *fbl = vedata->fbl;
	DefaultTextureList *dtxl = DRW_viewport_texture_list_get();
	EEVEE_TextureList *txl = vedata->txl;
	EEVEE_StorageList *stl = vedata->stl;
	EEVEE_PassList *psl = vedata->psl;
	EEVEE_PrivateData *g_data = stl->g_data;
	Scene *scene = draw_ctx->scene;

	float clear[4] = {0.0f, 0.0f, 0.0f, 0.0f};

	if (e_data.mist_sh == NULL) {
		char *frag_str = BLI_string_joinN(
		        datatoc_common_view_lib_glsl,
		        datatoc_common_uniforms_lib_glsl,
		        datatoc_bsdf_common_lib_glsl,
		        datatoc_effect_mist_frag_glsl);

		e_data.mist_sh = DRW_shader_create_fullscreen(frag_str, "#define FIRST_PASS\n");

		MEM_freeN(frag_str);
	}

	/* Create FrameBuffer. */
	DRW_texture_ensure_fullscreen_2D(&txl->mist_accum, GPU_R32F, 0); /* Should be enough precision for many samples. */

	GPU_framebuffer_ensure_config(&fbl->mist_accum_fb, {
		GPU_ATTACHMENT_NONE,
		GPU_ATTACHMENT_TEXTURE(txl->mist_accum)
	});

	/* Clear texture. */
	GPU_framebuffer_bind(fbl->mist_accum_fb);
	GPU_framebuffer_clear_color(fbl->mist_accum_fb, clear);

	/* Mist settings. */
	if (scene && scene->world) {
		g_data->mist_start = scene->world->miststa;
		g_data->mist_inv_dist = (scene->world->mistdist > 0.0f) ? 1.0f / scene->world->mistdist : 0.0f;

		switch (scene->world->mistype) {
			case WO_MIST_QUADRATIC:
				g_data->mist_falloff = 2.0f;
				break;
			case WO_MIST_LINEAR:
				g_data->mist_falloff = 1.0f;
				break;
			case WO_MIST_INVERSE_QUADRATIC:
				g_data->mist_falloff = 0.5f;
				break;
		}
	}
	else {
		float near = -sldata->common_data.view_vecs[0][2];
		float range = sldata->common_data.view_vecs[1][2];
		/* Fallback */
		g_data->mist_start = near;
		g_data->mist_inv_dist = 1.0f / fabsf(range);
		g_data->mist_falloff = 1.0f;
	}

	/* XXX ??!! WHY? If not it does not match cycles. */
	g_data->mist_falloff *= 0.5f;

	/* Create Pass and shgroup. */
	psl->mist_accum_ps = DRW_pass_create("Mist Accum", DRW_STATE_WRITE_COLOR | DRW_STATE_ADDITIVE);
	DRWShadingGroup *grp = DRW_shgroup_create(e_data.mist_sh, psl->mist_accum_ps);
	DRW_shgroup_uniform_texture_ref(grp, "depthBuffer", &dtxl->depth);
	DRW_shgroup_uniform_block(grp, "common_block", sldata->common_ubo);
	DRW_shgroup_uniform_vec3(grp, "mistSettings", &g_data->mist_start, 1);
	DRW_shgroup_call_add(grp, DRW_cache_fullscreen_quad_get(), NULL);
}

void EEVEE_mist_output_accumulate(EEVEE_ViewLayerData *UNUSED(sldata), EEVEE_Data *vedata)
{
	EEVEE_FramebufferList *fbl = vedata->fbl;
	EEVEE_PassList *psl = vedata->psl;

	if (fbl->mist_accum_fb != NULL) {
		GPU_framebuffer_bind(fbl->mist_accum_fb);
		DRW_draw_pass(psl->mist_accum_ps);

		/* Restore */
		GPU_framebuffer_bind(fbl->main_fb);
	}
}

void EEVEE_mist_free(void)
{
	DRW_SHADER_FREE_SAFE(e_data.mist_sh);
}
